The main problem at the house is there is no air intake. If we want to have the heating in the basement, we need to pull a new chimney tube.
What is wrong with the current chimney tube? It will oxidize if we use a condensation boiler.

The cheapest and best solution in his opinion is to put a small boiler of 50Kw at the second floor. This way, he pulls a aeration tube through the wall, and puts the boiler where the chimney is now.

The chimney on all floors can be removed then also.

He said a wall boiler, plus a water boiler fits within the case of the current chimney on that first floor. So we don't loose space.

Second floor with chimney case:

Another problem is the top floor boiler. He said this will never be OK, as you have 2 curves and 2 meter length until the chimney.
Because this boiler is almost at the top of the chimney this is way too far from it. His plan includes a water boiler to replace this also.